Hey my friend i have the same prob with my 1985 325e. Its been a nightmare. I had my alternator checked and it was good. Just for the heck of it i replaced it. It still wont charge the battery. My battery is good to. I have torn my whole dash apart looking for shorts in wires haven't found anything. I replaced my SI board cause a BMW enthusiast thought that could be it. still the prob is exists. let my know if you find something out if you would please, and i will let you know if i find anything out.